Tubular infrastructure including fluid conduits such as pipelines, risers and the like is commonly deployed subsea for the production of oil and gas from subterranean formations. Precipitation and build-up of unwanted deposits such as wax, hydrates and the like in such infrastructure is a common problem as a consequence of the relatively low temperatures in the subsea environment. Such build-up may reduce flow rates of hydrocarbon fluids through the infrastructure leading to a reduction in pressure and, in the worst case, total blockage of the infrastructure. As it becomes increasingly viable to produce oil and gas from hydrocarbon reservoirs located at greater sea depths, tubular infrastructure is increasingly being exposed to colder sea temperatures which exacerbate the problems of precipitation and build-up of unwanted deposits in the tubular infrastructure.
Depending on the particular geometry of the tubular infrastructure, different portions of the tubular infrastructure or different tubular components may be more susceptible to waxing than others. For example, bends in tubular infrastructure may be particularly susceptible to waxing because the change in direction of fluid flow at a bend may cause turbulence or recirculation of hydrocarbon fluids which results in the creation of a localised region of reduced fluid flow at the bend. Accordingly, it may be desirable to selectively control the amount of heat applied to different portions of tubular infrastructure or different tubular components used in the production of oil and gas particularly for tubular infrastructure or components for use in subsea environments.
Known methods for removing build-up from the interior of tubular infrastructure for oil and gas production include mechanical scraping or pigging methods, chemical methods, the use of pressure pulses, and heating of the hydrocarbon fluids and/or the subsea infrastructure. For example, US patent publication US 2010/0300486 relates to a known method for removal of solids that build-up in a system conduit containing or conveying fluid, especially to a method for removal of wax from pipelines and other equipment used for the transport of hydrocarbons. The method relies upon time-limited heating of the pipe to loosen wax deposits from an internal surface of the pipe and the transportation of the loosened wax as solid parts within a hydrocarbon fluid stream. The pipe may be heated electrically or using hot water. The method may be used with existing pipelines. The method may be used to clean wells. The method may be used to clean heat exchangers that are part of the top-side process equipment.
It is becoming more common to use composite tubulars for transporting hydrocarbons especially in subsea environments where such tubulars can provide a number of advantages over conventional steel tubulars. For example, US 2013/0108250 discloses a line for transporting a hydrocarbon. The line comprises a hollow tube having an electrically insulating outer surface, a heating layer with carbon fibres embedded in a polymer material, an electrical insulation layer arranged on the heating layer, a reinforcing layer with carbon fibres embedded in a polymer material arranged on the electrical insulation layer, and power supply means for feeding an electrical current to the heating layer for heating the tube. The power supply means may comprise a cable and a connection element which comes into contact with carbon fibres of the heating layer at a position adjacent to one end of the line, wherein the connection element is connected to the cable. In a different variant, the power supply means may comprise at least one receiving device connected to the heating layer and suitable for receiving a magnetic induction field and for generating electrical current.
Joining composite tubulars to one another or joining composite tubulars to other non-composite components such as other steel components is challenging. This is especially the case when joining composite tubulars in a subsea environment.